TARDISes usually moved through time and space by "disappearing there and reappearing here," (TV: Rose) a process known as "materialisation". This was controlled by a component called the dematerialisation circuit. (TV: Terror of the Autons) If a TARDIS' relative differentiator was missing or malfunctioning, then a TARDIS could only reappear in a different location in time, and not space. (COMIC: The Stolen TARDIS) TARDISes also could fly through space like conventional spacecraft, but doing so for prolonged periods could damage the ship, at least in the case of the Doctor's TARDIS. (TV: The Runaway Bride) A TARDIS was meant to have six pilots; (TV: Journey's End) however, the Doctor piloted the TARDIS on his own which led to it often jumping about in the Time Vortex and being an unpleasant ride for the passengers.

This sound was also made by other devices: SIDRATs, a craft similar to TARDISes used by the War Lords; (TV: The War Games) a Time Lord who appeared to the Third Doctor (without using any visible means of transport) to warn him of the appearance of the Master; (TV: Terror of the Autons) when the Time Lords provided the Third Doctor with a new dematerialisation circuit, it appeared on a table making this sound; (TV: The Three Doctors) and when the Fourth Doctor modified Skagra's invisible spaceship to travel like a TARDIS, again, this sound was heard. (HOMEVID: Shada)

If a TARDIS landed in the same space and time as another TARDIS, a time ram could occur, destroying both TARDISes, their occupants and even cause a black hole that would tear a hole in the universe — one the exact size of Belgium. (TV: The Time Monster, Time Crash). However, time rams could be avoided by materialising inside the other TARDIS. This act itself also had inherent dangers, including space loops. (TV: Logopolis, Space / Time).

Most TARDISes were used for the observation of various places and times. This kind of TARDIS underwent much modification over the years. Each new model received a distinct number to differentiate it from other models. The numerical scheme was seemingly simple; the higher the number, the later the design had been produced. [source needed] However, two types of numbering schemes may have been employed. The Monk called his version a "Mark 4", and the First Doctor's reaction seemed to suggest that he had a lower-numbered model. (TV: The Time Meddler) Subsequent incarnations and other Time Lords[who?] called the Doctor's TARDIS a "Type 40". (TV: The Deadly Assassin, The Ribos Operation et al.) According to the Teselecta's database, the Doctor's TARDIS was a "TT Type 40, Mark 3" (TV: Let's Kill Hitler)

By the time of the Doctor's fourth life, the entire Type 40 line had been retired from use. (TV: The Deadly Assassin) This policy ostensibly helped the Time Lords police time travel by reducing the total number of TT capsules in use at a given moment in time. Policing was further assisted by ensuring that individual units of the same model had the same key. Thus the Castellan's guards were able to easily effect entry into the Doctor's TARDIS. (TV: The Invasion of Time)

One of the key features of a TARDIS was that the interior existed in a dimension different from the exterior. The main application of this concept was that they were bigger on the inside than the outside. (TV: An Unearthly Child et al) This feature required use of "dimensional dams", which, upon the death of a TARDIS, would leak through. One such effect of this was the TARDIS exterior growing to a gargantuan size. (TV: The Name of the Doctor)

The Fourth Doctor once tried to explain the phenomenon to Leela by using two boxes, one smaller than the other. He placed the larger one further away, so it appeared as if it could fit within the small box. He then explained that if the big box could be accessed where it was from the small box, the small box would be "bigger on the inside". However, Leela dismissed this as "silly". (TV: The Robots of Death)

One feature of TARDISes was their ability to blend into their surroundings once they landed. If working properly, a chameleon circuit could assess the surroundings of a time and place just before arrival and change the exterior to resemble something common to that landscape. (TV: An Unearthly Child, Rose, Boom Town) On the one occasion that the Doctor temporarily got the chameleon circuit on his own TARDIS working again after leaving London in 1963, it selected forms very incongruous to its surroundings. (TV: Attack of the Cybermen) However, were the mechanism functioning correctly, it would have also been programmable from a keyboard on the TARDIS' main console. The Doctor once demonstrated to Adric how he would change the TARDIS into a pyramid, if the chameleon circuit were functioning properly.(TV: Logopolis) The Master was able to produce an architectural column in sometimes incongruous environments like the Pharos Project or Heathrow Airport (TV: Logopolis, Castrovalva, Time-Flight), and the Monk stated that he chose to make his TARDIS look like a Saxon altar. (TV: The Time Meddler) The Doctor once entered the Monk's TARDIS and changed its appearance from a pillar of stone to a police box identical to his own TARDIS. (TV: The Daleks' Master Plan)

When on Gallifrey, and presumably not utilising the chameleon circuit, some TARDISes were seen to resemble a plain rectangular cabinet with an outwards-sliding door on the front — a form also used by SIDRATs. (TV: The War Games) When the Doctor stole his Type 40 TARDIS from the repair shop, it and others nearby resembled stone cylindrical structures with sideways-sliding doors. (TV: The Name of the Doctor)

Even if in their first travels the First Doctor showed to be not fully aware of the conscience of his machine, (TV: The Edge of Destruction) since the Doctor's TARDIS displayed these organic traits, he considered it to be alive and even referred to it using feminine references. He talked to and stroked parts of the TARDIS when he operated it. (TV: School Reunion) He spoke of mechanical difficulties as medical or biological conditions like "indigestion" (TV: Doctor Who) and "digesting". (TV: The Runaway Bride) He once commented that a TARDIS was "more like a person". (TV: The Five Doctors) On one occasion, the Doctor's TARDIS manifested an avatar to help him fight a mental battle, taking on the forms and personas of the various companions who had ridden in it – however, this was when the Doctor was unconscious and battling within his own mind. (COMIC: The Forgotten)

When Chang Lee seemed to activate the Doctor's console upon leaning on a pillar and had the wooden doors to the Cloister Room open in front of him automatically, the Master explained that the TARDIS liked him. (TV: Doctor Who)

When the matrix of the Doctor's TARDIS was placed inside the body of Idris, it was shown that they were, in fact, sentient beings who did possess some degree of free will. The TARDIS said, in its human body, "All of my sisters are dead." (TV: The Doctor's Wife)

Before a TARDIS was fully functional, it needed to be primed with the biological imprint from the symbiotic nuclei of a Time Lord's cells. Known as the Rassilon Imprimatur, this gave them a symbiotic link to their TARDISes and allowed them to survive the physical stresses of time travel. Without the Imprimatur, molecular disintegration would result — a safeguard against misuse of time travel — even if the TARDIS technology were copied. Once a time machine was properly primed, however, and the imprint stored on a component (a briode nebuliser), it could be used safely by any species. (TV: The Two Doctors) If a TARDIS were to be used by anyone other than its owner and his familiars, it would assault their minds, which may lead to memory loss. (PROSE: Echoes of Future Past)

When the TARDIS needed more power to take off, rooms could be jettisoned to provide this power. This feature was used to escape both a gravity bubble and Event One (TV:Logopolis, Castrovalva), and to provide the extra power required to leave the universe entirely. (TV:The Doctor's Wife)

When the TARDIS was under attack from physical objects, the pilot could activate siege mode. This turned the exterior into a cube etched with Gallifreyan writing and sealed the entrance. (TV: Flatline)

An Index File provided text-based research into all manner of subjects relevant to TARDIS pilots and crew. This was accessible to Nyssa and Tegan. (TV: Castrovalva)

A voice interface could be requested for a variety of purposes. The TARDIS was able to communicate with its occupants using a holographic avatar, based on the Brigadier, and also created re-enactments of events from history, with characters based on the previous Doctors and their companions. (AUDIO: Zagreus) The Eleventh Doctor once got medical analysis and limited psychological counselling from this interface. (TV: Let's Kill Hitler)

A device compatible with 21st century Earth DVDs was capable of reading and executing automated piloting instructions for a TARDIS. (TV: Blink) It also could burn software to CD/DVD media for use on Earth computers. (TV: World War Three)

Psychic circuits kept a TARDIS linked to its crew when they left its interior, providing translation from alien languages and perhaps other features, so long as its attending Time Lord was in good health. (TV: The End of the World, The Christmas Invasion, et al)

While not technically a "renegade", Salyavin (a.k.a. Professor Chronotis) was said to have possessed a Type 12 TARDIS, with its controls appearing as simple panels hidden in an old book cupboard-type cabinet, and its control room "desktop" set as a university professor's library and study; his main TARDIS' disguise was that of his quarters at Cambridge University (HOMEVID: Shada)

Is "TARDIS" somehow "more correct" than "Tardis"? It's an open question, really. Here's what can be safely said.

The acronym was introduced into written English as "Tardis". The earliest Doctor Who publications — like 1960s Doctor Who annuals — consistently styled it as the ordinary word "Tardis", capitalising the T and often italicising the word in deference to the fact that it was a ship name. As David J. Howe and friends once noted in a behind-the-scenes exploration of An Unearthly Child:

This explains why World Distributors' Doctor Who annuals often styled the name Tardis, not TARDIS, TARDIS or even "the Tardis". Common sentences in early 1960s annuals ran along the lines of, "The Doctor made his way back to Tardis, where Ben and Polly were waiting for him."

World eventually stopped italicising Tardis, but they used "Tardis" throughout their stewardship of the Doctor Who annuals, with the form being used as late as their final edition in 1986.

Similarly, Radio Times listings have always treated the acronym like a regular word. Even in the 21st century, "Tardis" is the form found in dictionaries, such as the Oxford American Dictionary. Like laser and sonar, then, "Tardis" is what some linguists call an anachronym. Since most of the general public doesn't know that it is an acronym, its heritage as an acronym is viewed as anachronistic, and therefore forgotten.

That said, a few generalisations can be noted. Throughout most of the classic run — at least prior to John Nathan-Turner, the preferred form was Tardis. Thus, in Target novelisations, annuals, and other printed material that was actually contemporaneous with the original version of Doctor Who, Tardis is the form of choice.

Nevertheless, despite the increased use of "TARDIS" in prose fiction, there still is no firm preference expressed by narratives in visual media like television episodes and comic stories. Where the word has appeared, it has done so along other words exclusively set in the uppercase. For instance, in the plaque installed on the Eleventh Doctor's TARDIS set, all the words are in uppercase, so nothing can be inferred about the "proper" way to capitalise the acronym. Equally, in Let's Kill Hitler, the word appears on a screen where all other text is in uppercase. Comic depictions have also been lettered in all uppercase, as is standard for the medium.